This application is based on Japanese Patent Application No. 2001-31255 filed on Feb. 7, 2001, and Japanese Patent Application No. 2002-9956 filed on Jan. 18, 2002 the contents of which are incorporated herein by reference.
1. Field of the Invention
The invention relates to a fuel injection pump for an internal combustion engine for a vehicle.
2. Description of Related Art
Conventionally, a fuel injection pump that has an eccentric cam and a cam-ring is known in the art. The cam-ring orbits around a rotating axis or a center axis of the camshaft and drives plungers reciprocally to pressurize fuel in a pressurizing chamber.
The cam-ring has a metal bush for preventing the cam from a sticking. However, it is necessary to select material of the metal bush to improve an anti-sticking performance. It is also effective to improve the anti-sticking performance by enlarging a surface of the metal bush to dissipate a surface pressure.
However, utilizing a high-performance material increases the costs of the apparatus. The large metal bush is also expensive and makes it difficult to reduce the size of the pump.
It is an object of the present invention to provide a fuel injection pump being capable of reducing an abrasion and reducing possibilities of a sticking.
It is further object of the present invention to provide a fuel injection pump being capable of improving a lubricity.
According to a first aspect of the present invention, the cam has a concave portion on an outer surface of the cam. The concave portion introduces a lubricant into a gap between the cam and the cam-ring. The concave portion is formed on a region where a force caused by pressurizing fuel is not applied. The cam pushes the cam-ring by an outer surface on a region where a distance between the rotating axis of the cam and an outer profile increases. The region where the force caused by pressurizing fuel is not applied is generally located on a slightly retard side from a region where the distance between the rotating axis and the outer profile decreases. Even in the case that the cam drives a plurality of plungers, the cam has the region where the force caused by pressurizing fuel is not applied. The concave portion introduces fuel to improve the lubricity. Even if the concave portion has an edge, since the force doesn""t concentrate on the edge, it is possible to reduce an abrasion.
The concave portion may be a groove extending over an axial direction of the cam from an axial end of the cam to the other axial end of the cam. This arrangement may introduce more lubricant.
The groove may not be in parallel with a rotating axis of the cam. This arrangement may increase lubricant flow in the groove.
The concave portion may be formed on a region from a top dead center to a bottom dead center in a rotating direction.